Semiconductor chips are fabricated on suitable flat substrate wafers, such as GaAs, diamond coated substrates, silicon carbide, and silicon wafers. After making the active devices, a series of steps are performed to connect the various devices with highly conducting wiring structures so they can have communication with each other to perform logic operations. These wiring structures or interconnect structures are essentially a skeletal network of conducting materials, typically metals in a matrix of dielectric materials. In high performance devices and to improve device density and yield, it is imperative to minimize topographic features and dimensions within the interconnect layers for any given device and across the entire substrate.
Wire drawing operations to fabricate wire bond materials reduce the grain size of the drawn wire. While the drawing operation typically increases the mechanical strength of the drawn wire, it also aligns the grains of the wire along the drawing direction. The alignment of the grains detrimentally increases the resistivity of the drawn material from its native value. A typical method to recover the resistivity of the drawn wire is to anneal it at a high temperature to enlarge the grains of the microstructure of the wire. However, the annealing process also weakens the material. The annealed wire can break easily by grain boundary sliding. Annealed wires tend to break at their mid span during wire bond operations. To improve the strength of the wire, the wire material is usually strengthened by the introduction of very small amount of dopants (e.g. Si and/or Be) into the structure of the wire. Excess dopants, however, may further harden the wire thus making it brittle. Thus, conventional wire structures often suffer for a lack of strength, decreased conductivity, or both.
There is also a continuing need to decrease the dimensions of wires, especially bonding wires. Conventional wires often include a metal filament for carrying the signal and an insulative plastic sheath encasing the filament to prevent electrical shorts. The sheath is usually flexible and slides over the filament to accommodate shearing as the wire is bent. In general, the strength of the wire structure is determined by the thickness of the filament. To that end, conventional wire structures typically have a relatively large diameter to meet the strength and reliability requirements. In many applications, the wire is thicker than necessary to carry the electrical signal in order to achieve the desired strength characteristics.
What is needed is a device and methods which overcome the above and other disadvantages of known wire structures.